Bearings are used for many different applications. Spherical roller bearings are bearings which contain an outer race, an inner race, and a plurality of freely rotatable spherical roller elements positioned between the two races. The inner race further contains a taper bore formed on the interior diameter thereof which is designed to mate with a taper machined into the shaft on which it is to be mounted. Spherical roller bearings are commonly used by the printing industry and by manufacturers employing rotary die cutters. Rotary die cutters can be used to cut many different kinds of materials. Normally, a pair of spherical roller bearings are used to rotatably mount a rotary die cutter onto a shaft which is then assembled into a die cutting module. When using such bearings, it is important that the bearings be precisely preloaded so as to provide a precision mounting of the rotary die cutter and also to extend the life of the bearing.
As stated above, the tapered bore on the internal diameter of a spherical roller bearing is designed to match up with a taper machined into the shaft onto which the bearing will be mounted. For those operations wherein a rotary die cutter is employed, a shaft will have the rotary die cutter mounted in the center thereof and will contain a pair of tapered surfaces, each located adjacent to one side of the die cutter. A shoulder is machined into the shaft adjacent to each tapered surface and a threaded portion is machined into the shaft adjacent to the tapered portions. A metal shim is slid onto the shaft and is positioned adjacent to the shoulder. The spherical roller bearings are then positioned onto the tapered surfaces. The thickness of each shim will dictate the distance an adjacent bearing will be able to move up the tapered surface. A lock nut is then threaded onto each end of the shaft and each lock nut will contact the inner race of one of the bearings. As the inner race of each bearing expands, it causes the bearing to be preloaded on the shaft. The lateral distance the bearing moves up the tapered surface is determined by the thickness of the metal shim which has been slid onto the shaft. If the bearing is not sufficiently preloaded, it will be sloppy and the shaft it is supporting will not revolve with the required precision. Conversely, if the bearing is excessively preloaded, it will fail prematurely requiring expensive downtime and replacement.
Today, many different methods are used to preload a bearing onto a shaft. Two common methods include the use of a bearing gauge and gauge blocks which are used to determine the proper shim thickness required to set the bearing preload. This method works well on brand new bearings but cannot be used to preload reconditioned bearings. A second method involves the use of a string which is wrapped around the outer race of a bearing after it has been secured in place by the lock nut. The free end of the string is attached to a spring scale, similar to those used to weigh fish. As the string is pulled, the resistance of the roller elements of the bearing can be felt. This method is very subjective to human error and therefore tends to be inaccurate, especially when performed by an inexperienced operator. Although this method does work on both new and reconditioned bearings, it will not work when the bearings are packed with certain synthetic greases which do not have an extreme pressure additive.
Now, an apparatus and method have been invented for precisely preloading a new or reconditioned bearing onto a shaft. The apparatus and method also work on bearings which have been packed with certain synthetic greases which do not have an extreme pressure additive.